package com.tensai.study.java.basic.algorithm.encrypt;

import org.apache.commons.codec.binary.Base64;

import javax.crypto.Cipher;
import java.nio.charset.StandardCharsets;
import java.security.*;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;

/**
 * RSA 加密 （公钥私钥 ）
 *
 * @author Tensai
 */
public class RsaEncrypt {
	/**
	 * 用于封装随机产生的公钥与私钥
	 */
	private static final Map<Integer, String> KEY_MAP = new HashMap<>();

	public static void main(String[] args) throws Exception {
		//生成公钥和私钥
		genKeyPair();
		//加密字符串
		String message = "df723820";
		System.out.println("随机生成的公钥为:" + KEY_MAP.get(0));
		System.out.println("随机生成的私钥为:" + KEY_MAP.get(1));
		String messageEn = encrypt(message, KEY_MAP.get(0));
		System.out.println(message + "\t加密后的字符串为:" + messageEn);
		String messageDe = decrypt(messageEn, KEY_MAP.get(1));
		System.out.println("还原后的字符串为:" + messageDe);
	}

	/**
	 * 随机生成密钥对
	 *
	 * @throws NoSuchAlgorithmException 异常
	 */
	private static void genKeyPair() throws NoSuchAlgorithmException {
		// KeyPairGenerator类用于生成公钥和私钥对，基于RSA算法生成对象
		KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA");
		// 初始化密钥对生成器，密钥大小为96-1024位
		keyPairGen.initialize(512, new SecureRandom());
		// 生成一个密钥对，保存在keyPair中
		KeyPair keyPair = keyPairGen.generateKeyPair();
		// 得到私钥
		RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
		// 得到公钥
		RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
		String publicKeyString = new String(Base64.encodeBase64(publicKey.getEncoded()));
		// 得到私钥字符串
		String privateKeyString = new String(Base64.encodeBase64((privateKey.getEncoded())));
		// 将公钥和私钥保存到Map
		//0表示公钥
		KEY_MAP.put(0, publicKeyString);
		//1表示私钥
		KEY_MAP.put(1, privateKeyString);
	}

	/**
	 * RSA公钥加密
	 *
	 * @param str       加密字符串
	 * @param publicKey 公钥
	 * @return 密文
	 * @throws Exception 加密过程中的异常信息
	 */
	private static String encrypt(String str, String publicKey) throws Exception {
		//base64编码的公钥
		byte[] decoded = Base64.decodeBase64(publicKey.getBytes());
		RSAPublicKey pubKey = (RSAPublicKey) KeyFactory.getInstance("RSA").generatePublic(new X509EncodedKeySpec(decoded));
		//RSA加密
		Cipher cipher = Cipher.getInstance("RSA");
		cipher.init(Cipher.ENCRYPT_MODE, pubKey);
		// TODO 升级后未验证
		return Arrays.toString(Base64.encodeBase64(cipher.doFinal(str.getBytes(StandardCharsets.UTF_8))));
	}

	/**
	 * RSA私钥解密
	 *
	 * @param str        加密字符串
	 * @param privateKey 私钥
	 * @return 铭文
	 * @throws Exception 解密过程中的异常信息
	 */
	private static String decrypt(String str, String privateKey) throws Exception {
		//64位解码加密后的字符串
		byte[] inputByte = Base64.decodeBase64(str.getBytes(StandardCharsets.UTF_8));
		//base64编码的私钥
		byte[] decoded = Base64.decodeBase64(privateKey.getBytes());
		RSAPrivateKey priKey = (RSAPrivateKey) KeyFactory.getInstance("RSA").generatePrivate(new PKCS8EncodedKeySpec(decoded));
		//RSA解密
		Cipher cipher = Cipher.getInstance("RSA");
		cipher.init(Cipher.DECRYPT_MODE, priKey);
		return new String(cipher.doFinal(inputByte));
	}

}



